The present invention relates to a method of producing oxide superconductor composite materials. More specifically, the invention relates to a novel method of producing oxide superconductor composite materials which are useful as superconducting wires, such as various superconducting magnets, superconducting transmission cables, or magnetic shields, used in superconducting equipment, which have higher critical current densities than those of previously known materials, and can easily be produced.
The 2212 phase and the 2233 phase known as Bi oxide high-temperature superconductors have been actively studied to achieve practical use as superconducting wires.
Various methods including a coating method and a silver sheathing method have been formerly proposed, for producing wires of oxide superconductors. In all such methods, a combination of a metallic substrate (such as silver) and an oxide superconductor has been employed. For a bismuth 2212 (Bi2Sr2CaCu2Ox) wire, regardless of the method chosen, in order to obtain a wire of excellent characteristics, with high critical current density, the material is first heated above the decomposition temperature of bismuth 2212 to provide a partially molten state, then is either slowly cooled, or the atmosphere (temperature or oxygen pressure) is controlled to change the solidification point. Crystals are again grown to obtain an oriented structure required to provide high critical current density. However, in such methods, the characteristics are much influenced by the state of the partial melt. Therefore, the permissible range of the temperature for heat treatment to provide excellent characteristics, becomes as narrow as xc2x12xc2x0 C. the optimum temperature. Thus, it must be said that this method has technical problems when applied to the production of large-sized products. Therefore, overcoming such technical difficulties in producing large-sized products without decreasing the characteristics, by widening the permissible range of the heat treatment temperature, and reducing the cost by improving yield, are important goals.
In view of the above situation, the present invention has been invented as a result of intensive study, and its main object is to provide a novel method which allows easy production of a superconducting composite material for a wire having excellent productivity and higher critical current density.